Friday, August 7, 2015

EMP Trash Can Faraday Cage Testing in Lab

ests are conducted to measure how effective metal garbage cans are at blocking high-frequency energy, such as that released by an high-altitude nuclear electromagnetic pulse (EMP). Tips are provided on how to greatly improve the shielding effectiveness.


Joe said...

Worth a look.

A standard steel garbage can by itself is NOT enough to prevent your your expensive (comm. radio, laptop computer, digital camera, hobby drone, night vision optic, etc...etc... ) from literally becoming useless paperweights during any type
of serious EMP event.

The good news shown on this video is that a very simple and fairly cost effective modification quickly solves your e-gear storage problems.

Anonymous said...

And what difference would there be in shielding if you GROUNDED the trash can?
I'll have to look for more from the Doctor.
Seeing as I have a fair amount of time and money invested in various electronics, this would be worthwhile.

B Woodman

Anonymous said...

I say gather all your electronics close, stick your head in the metal can, attach to 220V outlet. Wait for the apocalypse.

Anonymous said...

Grounding is not foolproof, as EMPs can come in through the ground as well. Sometimes, depending on where the strike is, grounding can actually be the source of EMPs.

JC Dodge said...

I saw this demonstrated by a company out of the Harpers Ferry WV area, at a survival expo two years ago. They build Faraday cages for the .Gov, and have come up with a number of improvised items to use, and have tested them all with their EMP generator.

Historian said...

Layering is your friend. Alternate layers of conductive and non-conductive material add about 20 to 30 db of attenuation for each layer of conductive material. (brown paper or poly plastic, followed by extra heavy duty aluminium foil, repeat as needed) Your goal is reducing the signal to well under 1 volt per meter. Allowing for a 2x safety factor, this means you need at least 90 to 100 db total attentuation, so you will need 4 or 5 layers to be reasonably sure of success.

And grounding does not help the performance of a Faraday cage.

Bad Cyborg said...

We had a nice faraday cage in the first radio shop I worked in after tech school. It was a good 15' on a side and 10' high made of old fashioned metal window screening (shite on my windows here is plastic) and well grounded - as in copper rods at the corners driven 5 yards into the earth. We had to align sensitive receivers 2 blocks away from 10KW UHF and VHF transmitters and needed ambient noise to be in the fractional millivolt range - like they were way the hell out in the country instead of just down the street from the transmitters they had to receive. IMS they had multiple layers, each insulated from the other and each separately grounded. Some fool negligently drove a slotted screwdriver through all the layers on one side and it was a stone bitch to fix. Dumbass lost a coupla stripes IMS, along with most of the meat and hide on his ass. I also seem to remember him leaving the radio shop and transferring to Civil Engineers Squadron. Something about a job picked up completely via on-the-job training w/o any tech school. Kinda sad, almost. Nine lovely months at Keesler AFB (AKA the pimple in the armpit of the Air Force) and he winds up a shovel jockey in CES.

As long as the gaps in the conductive material is a sub-multiple of the wavelength of what you are trying to shield from you should be ok. Trick is to keep the layers from grounding into each other or you lose the effect of layering (hence Historian's butcher paper or poly plastic alternating with heavy duty aluminum. just make sure they do not interconnect electrically BEFORE the ground straps.

For Anon @ 0918: you still want the thing grounded. You know what you cal alternating layers of aluminum foil and sheet plastic? A honking big (think multiple FARADS) CAPACITOR! There is a formula for capacitance based upon square area of plates (i.e. the conductive sheets) and the dialectric constant of the insulator (butcher paper or sheet plastic). Google "leyden jar". Big glass (old fashioned mayonnaise) jar with tin foil inside and out. Early primitive capacitors. Can store a huge (many, many jules) amount of electricity. IMS some early experimenters managed to electrocute themselves with the things - and this before ever flew his kite or we knew how to generate electricity.

The only "EMP" I ever heard about propagating through the ground lead is from lighting strikes. And if anyone is wondering why we go to the trouble to build a faraday cage instead of insulating the equipment, it is because there is no insulation for magnetic fields. There are certain materials which block electrical current - they call them dielectrics - but while dimagnetic material is theoretically possible nobody has found one to date. Figure out how to make a working dimagnetic and you could buy and sell Trump, Gates and the entire Arabian Peninsula out of pocket change. But I still don't think you could convince Gates to be a conservative or the Donald to lose the combover. You just might be able to tell Trump to STFU - but I doubt you could make it stick more than a minute or two.

josephpmartino said...

Don't trust a metal ammo can to be a Faraday shield. To begin with, the rubber gasket inside the lid is nonconductive. It seals out water, but prevents a good electrical connection between the lid and the rest of the can. Using metallic tape won't help, because the paint on the can is also nonconductive.

If you want to use a metal ammo can, sand off the paint around the outside of the lid, and a corresponding patch below the lid, then use the conductive tape.

Bob Earle said...

That's what I always do. Use a round steel wire brush on a drill and grind off the paint around the inside of the gasket seal point on the lid and run conductive adhesive aluminum or copper tape all around it, over the rubber gasket, making sure it has metal contact all the way around on the inside of the gasket. Then I grind off the paint just on the top edge of the bottom box. When the box is closed, the metal tape contacts with the bare metal upper edge of the box and is itself connected to bare metal all around the inside of the lid gasket. I leave the rubber gasket underneath to ensure good pressure on the tape into the bare upper edge of the box.